Refrigeration and air conditioning systems are commonly configured with means for system capacity control, thereby allowing the systems to improve temperature control accuracy, reliability, and energy efficiency.
Currently the most common means of refrigerant system capacity control is accomplished by unit cycling (turning the compressor on and off in response to fluctuations in temperature or system pressure). However, unit cycling does not allow for tight temperature control, and therefore, commonly creates discomfort and/or undesired temperature variations in the conditioned/refrigerated space.
A suction modulation valve located on a suction line downstream of the compressor is another means commonly utilized for system capacity control. However, suction modulation valves are expensive and are inefficient for system capacity control.
A hot gas bypass unloader valve integral to the compressor can be used to control compressor capacity, and hence, refrigeration and air conditioning system capacity. The bypass unloader valve operates to re-circulate refrigerant vapor from the discharge plenum back to the suction plenum. Thus, there is no compression generated flow of refrigerant out of the cylinder when the bypass unloader valve is actuated. Unfortunately, bypass unloader valves only control compressor (and system) capacity in distinct increments or modes. For example, in a four cylinder compressor with two pairs of cylinders, a fifty percent capacity reduction is achieved by actuating the bypass unloader valve adjacent one of the two pairs of cylinders. However, a capacity reduction of, for example, twenty five percent could not be achieved in the four cylinder compressor with the bypass unloader valve. Thus, optimal control of compressor capacity, and hence, the refrigerated or air conditioned environment cannot be achieved with current bypass unloader valve technology.